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ABSTRACT: Understanding the influence of growth temperature and carbon dioxide (CO2) on seed quality in terms of seed composition, subsequent seedling emergence and early seedling vigour is important under present and future climates. The objective of this study was to determine the combined effects of elevated temperature and CO2 during seed-filling of parent plants on seed composition, subsequent seedling emergence and seedling vigour of red kidney bean (Phaseolus vulgaris). Plants of cultivar ‘Montcalm’, were grown at daytime maximum/nighttime minimum sinusoidal temperature regimes of 28/18 and 34/24 °C at ambient CO2 (350 μmol mol−1) and at elevated CO2 (700 μmol mol−1) from emergence to maturity. Seed size and seed composition at maturity and subsequent per cent emergence, early seedling vigour (rate of development) and seedling dry matter production were measured. Elevated CO2 did not influence seed composition, emergence, or seedling vigour of seeds produced either at 28/18 or 34/24 °C. Seed produced at 34/24 °C had smaller seed size, decreased glucose concentration, but significantly increased concentrations of sucrose and raffinose compared to 28/18 °C. Elevated growth temperatures during seed production decreased the subsequent per cent emergence and seedling vigour of the seeds and seedling dry matter production of seed produced either at ambient or elevated CO2.
Journal of Agronomy and Crop Science 03/2009; 195(2):148 - 156. · 2.43 Impact Factor
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ABSTRACT: Rice (Oryza sativa L. cv. IR-72) and soybean (Glycine max L. Merr. cv. Bragg), which have been reported to differ in acclimation to elevated CO2, were grown for a season in sunlight at ambient and twice-ambient [CO2], and under daytime temperature regimes ranging from 28 to 40°C. The objectives of the study were to test whether CO2 enrichment could compensate for adverse effects of high growth temperatures on photosynthesis, and whether these two C3 species differed in this regard. Leaf photosynthetic assimilation rates (A) of both species, when measured at the growth [CO2], were increased by CO2 enrichment, but decreased by supraoptimal temperatures. However, CO2 enrichment more than compensated for the temperature-induced decline in A. For soybean, this CO2 enhancement of A increased in a linear manner by 32–95% with increasing growth temperatures from 28 to 40°C, whereas with rice the degree of enhancement was relatively constant at about 60%, from 32 to 38°C. Both elevated CO2 and temperature exerted coarse control on the Rubisco protein content, but the two species differed in the degree of responsiveness. CO2 enrichment and high growth temperatures reduced the Rubisco content of rice by 22 and 23%, respectively, but only by 8 and 17% for soybean. The maximum degree of Rubisco down-regulation appeared to be limited, as in rice the substantial individual effects of these two variables, when combined, were less than additive. Fine control of Rubisco activation was also influenced by both elevated [CO2] and temperature. In rice, total activity and activation were reduced, but in soybean only activation was lowered. The apparent catalytic turnover rate (Kcat) of rice Rubisco was unaffected by these variables, but in soybean elevated [CO2] and temperature increased the apparent Kcat by 8 and 22%, respectively. Post-sunset declines in Rubisco activities were accelerated by elevated [CO2] in rice, but by high temperature in soybean, suggesting that [CO2] and growth temperature influenced the metabolism of 2-carboxyarabinitol-1-phosphate, and that the effects might be species-specific. The greater capacity of soybean for CO2 enhancement of A at supraoptimal temperatures was probably not due to changes in stomatal conductance, but may be partially attributed to less down-regulation of Rubisco by elevated [CO2] in soybean than in rice. However, unidentified species differences in the temperature optimum for photosynthesis also appeared to be important. The responses of photosynthesis and Rubisco in rice and soybean suggest that among C3 plants species-specific differences will be encountered as a result of future increases in global [CO2] and air temperatures.
Plant Cell and Environment 06/2008; 20(1):68 - 76. · 5.22 Impact Factor
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ABSTRACT: Rising atmospheric carbon dioxide concentration ([CO2]) has generated considerable interest in the response of agricultural crops to [CO2]. The objectives of this study were to determine the effects of a wide range of daytime [CO2] on dark respiration of rice (Oryza sativa L. cv. IR-30). Rice plants were grown season-long in naturally sunlit plant growth chambers in subambient (160 and 250), ambient (330), or super-ambient (500, 660 and 900 μmol CO2 mol−1 air) [CO2] treatments. Canopy dark respiration, expressed on a ground area basis (Rd) increased with increasing [CO2] treatment from 160 to 500 μmol mol−1 treatments and was very similar among the superambient treatments. The trends in Rd over time and in response to increasing daytime [CO2] treatment were associated with and similar to trends previously described for photosynthesis. Specific respiration rate (Rdw) decreased with time during the growing season and was higher in the subambient than the ambient and superambient [CO2] treatments. This greater Rdw in the subambient [CO2] treatments was attributed to a higher specific maintenance respiration rate and was associated with higher plant tissue nitrogen concentration.
Plant Cell and Environment 04/2006; 15(2):231 - 239. · 5.22 Impact Factor
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ABSTRACT: Peanut (Arachis hypogaea) crops in Benin often experience late leafspot (Cercosporidium personatum), which causes severe yield losses associated with leaf defoliation and necrosis. The objective of this research was to determine the best method of disease assessment and to test its utility in the CROPGRO-peanut model to simulate growth and yield as affected by late leafspot in early and late maturing peanut cultivars grown at different sowing dates under rain-fed conditions (without irrigation) in northern Benin. Two peanut cultivars TS 32-1 and 69–101 were sown on three dates between May and August during 1998 and 1999. In both years there was severe occurrence of late leafspot and the progression of disease was earlier and faster with later sowing dates. Overall, the long duration cultivar 69–101 produced greater yield than the short duration cultivar TS 32-1. The CROPGRO-peanut model was able to predict and simulate the observed crop and pod dry matter over time when input on percent diseased leaf area and percent defoliation were provided. Of several disease assessments, the best approach was to input measured percent main-stem defoliation above the fourth node and percent diseased leaf area estimated from visual leafspot score.
Annals of Applied Biology 06/2005; 146(4):469 - 479. · 2.18 Impact Factor
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ABSTRACT: Genetic modifications of agronomic crops will likely be necessary to cope with global climate change. This study tested the hypotheses that genotypic differences in rice (Oryza sativa L.) leaf photosynthesis at elevated [CO2] and temperature are related to protein and gene expression of Rubisco, and that high growth temperatures under elevated [CO2] negatively affect photosystem II (PSII) photochemical efficiency. Two rice cultivars representing an indica (cv. IR72) and japonica type (cv. M103) were grown in 350 (ambient) and 700 (elevated) µmol CO2 mol−1 at 28/18, 34/24 and 40/30 °C sinusoidal maximum/minimum, day/night temperatures in outdoor, sunlit, environment-controlled chambers. Leaf photosynthesis of IR72 favoured higher growth temperatures more than M103. Rubisco total activity and protein content were negatively affected in both genotypes by high temperatures and elevated CO2. However, at moderate to high growth temperatures, IR72 leaves averaged 71 and 39% more rbcS transcripts than M103 under ambient and elevated CO2, respectively, and likewise had greater Rubisco activity and protein content. Expression of psbA (D1 protein of PSII) in IR72 leaves increased with temperature, whereas it remained constant for M103, except for a 20% decline at 40/30 °C under elevated CO2. Even at the highest growth temperatures, PSII photochemical efficiency was not impaired in either genotype grown under either ambient or elevated CO2. Genotypic differences exist in rice for carboxylation responses to elevated CO2 and high temperatures, which may be useful in developing genotypes suited to cope with global climate changes.
Plant Cell and Environment 11/2003; 26(12):1941 - 1950. · 5.22 Impact Factor
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New Phytologist 04/2002; 154(1):77 - 84. · 6.64 Impact Factor
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ABSTRACT: Rice plants (Oryza saliva L., cv. IR30) were grown in paddy culture in outdoor, naturally sunlit, controlled-environment, plant growth chambers at Gainesville, Florida, USA, in 1987. The rice plants were exposed throughout the season to subambient (160 and 250), ambient (330) or superambient (500, 660, 900 μmol CO2/mol air) CO2 concentrations. Total shoot biomass, root biomass, tillering, and final grain yield increased with increasing CO2 concentration, thegreatest increase occurring between the 160 and 500 μmol CO2/mol air treatments. Early in the growing season, root:shoot biomass ratio increased with increasing CO2 concentration; although the ratio decreased during the growing season, net assimilation rate increased with increasingCO2 concentration and decreased during the growing season. Differences in biomass and lamina area among CO2 treatments were largely due to corresponding differences in tillering response. The number of panicles/plant was almost entirely responsible for differences in final grain yield among CO2 treatments. Doubling the CO2 concentration from 330 to 660 μmol CO2/mol air resulted in a 32 % increase in grain yield. These results suggest that important changes in the growth and yield of rice may be expected in the future as the CO2 concentration of the earth's atmosphere continues to rise.
The Journal of Agricultural Science 11/1990; 115(03):313 - 320. · 2.04 Impact Factor
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ABSTRACT: It is important to understand the effects of environmental conditions during plant growth on longevity and temperature response of pollen. Objectives of this study were to determine the influence of growth temperature and/or carbon dioxide (CO2) concentration on pollen longevity and temperature response of peanut and grain sorghum pollen. Plants were grown at daytime maximum/nighttime minimum temperatures of 32/22, 36/26, 40/30 and 44/34 °C at ambient (350 μmol mol−1) and at elevated (700 μmol mol−1) CO2 from emergence to maturity. At flowering, pollen longevity was estimated by measuring in vitro pollen germination at different time intervals after anther dehiscence. Temperature response of pollen was measured by germinating pollen on artificial growth medium at temperatures ranging from 12 to 48 °C in incubators at 4 °C intervals. Elevated growth temperature decreased pollen germination percentage in both crop species. Sorghum pollen had shorter longevity than peanut pollen. There was no influence of CO2 on pollen longevity. Pollen longevity of sorghum at 36/26 °C was about 2 h shorter than at 32/22 °C. There was no effect of growth temperature or CO2 on cardinal temperatures (Tmin, Topt, and Tmax) of pollen in both crop species. The Tmin, Topt, and Tmax identified at different growth temperatures and CO2 levels were similar at 14.9, 30.1, and 45.6 °C, respectively for peanut pollen. The corresponding values for sorghum pollen were 17.2, 29.4, and 41.7 °C. In conclusion, pollen longevity and pollen germination percentage was decreased by growth at elevated temperature, and pollen developed at elevated temperature and/or elevated CO2 did not have greater temperature tolerance.Research highlights?Elevated temperature decreased pollen germination and pollen longevity. ?There was no influence of elevated carbon dioxide (CO2) on pollen longevity. ?Sorghum pollen had shorter longevity than peanut pollen. ?Pollen developed at elevated elevated CO2 did not have greater temperature tolerance. ?Cardinal temperatures of pollen grains were not affected by temperature or CO2.
Environmental and Experimental Botany 70(1):51-57. · 2.98 Impact Factor
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ABSTRACT: Spikelet fertility (seed-set) is an important component of yield that is sensitive to high temperature. The objectives of this research were (a) to quantify the effects of high temperature on spikelet fertility and harvest index of rice; (b) to determine if there were species, ecotype, and/or cultivar differences in response to high temperature; and (c) to understand the reasons for lower and/or differential spikelet fertility and harvest index of rice cultivars at high temperatures. Fourteen rice cultivars of different species (Oryza sativa and Oryza glaberrima), ecotypes (indica and japonica) and origin (temperate and tropical) were exposed to ambient and high temperature (ambient + 5 °C) at Gainesville, Florida. High temperature significantly decreased spikelet fertility across all cultivars, but effects varied among cultivars. Based on decreases in spikelet fertility at high temperature, cultivar N-22 was most tolerant, while cultivars L-204, M-202, Labelle, Italica Livorna, WAB-12, CG-14 and CG-17 were highly susceptible and cultivars M-103, S-102, Koshihikari, IR-8 and IR-72 were moderately susceptible to high temperature. There were no clear species or ecotype differences, as some cultivars in each species or within ecotypes of tropical and temperature origin were equally susceptible to high temperature (for example M-202 temperate japonica, Labelle tropical japonica, CG-14 O. glaberrima, and WAB-12 interspecific). Decreased spikelet fertility and cultivar difference at high temperature were due mainly to decreased pollen production and pollen reception (pollen numbers on stigma). Lower spikelet fertility at elevated temperature resulted in fewer filled grains, lower grain weight per panicle, and decreased harvest index. There is a potential for genetic improvement for heat tolerance, thus it is important to screen and identify heat-tolerant cultivars. Spikelet fertility at high temperature can be used as a screening tool for heat tolerance during the reproductive phase.
Field Crops Research.
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ABSTRACT: Integrated use of organic and inorganic fertilizers can improve crop productivity and sustain soil health and fertility. The present research was conducted to study the effects of application of green manures [sesbania (Sesbania aculeate Poiret) and crotalaria (Crotalaria juncea L.)] and farmyard manure on productivity of rice (Oryza sativa L.) and its residual effects on subsequent groundnut (Arachis hypogaea L.) crop. Rice and groundnut crops were grown in sequence during rainy and post-rainy seasons with and without green manure in combination with different fertilizer and spacing treatments under irrigated conditions. The results showed that application of green manures sesbania and crotalaria at 10 t ha−1 to rice compared to no green manure application significantly increased grain yield of rice by 1.6 and 1.1 t ha−1, and pod yields of groundnut crop succeeding rice by 0.25 and 0.16 t ha−1, respectively. There was no significant difference between the application of crotalaria or farmyard manure at 10 t ha−1 on grain yields of rice, but pod yields of subsequent groundnut crop were greater with application of green manure. There was no significant effect of different spacing 20×15,15×15,15×10 cm2 (333 000; 444 000; 666 000 plant ha−1, respectively) on grain yield of rice. Pod yields of groundnut were significantly greater with closer spacing 15×15 cm2 (444 000 plants ha−1) as compared to spacing of 30×10 cm2 (333 000 plants ha−1). Maximum grain of rice was obtained by application of 120:26:37 kg NPK ha−1 in combination with green manures, whereas maximum pod yield of groundnut was obtained by residual effect of green manure applied to rice and application of 30:26:33 kg NPK ha−1 in combination with gypsum applied to groundnut crop.
Field Crops Research.
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ABSTRACT: The current increase in atmospheric carbon dioxide concentration ([CO2]) along with predictions of possible future increases in global air temperatures have stimulated interest in the effects of [CO2] and temperature on the growth and yield of food crops. This study was conducted to determine the effects and possible interactions of [CO2] and temperature on the growth and yield of rice (Oryza saliva L., cultivar IR-30). Rice plants were grown for a season in outdoor, naturally sunlit, controlled-environment, and plant growth chambers. Temperature treatments of 28/21/25, 34/27/31, and 40/33/37°C (daytime dry bulb air temperature/night-time dry bulb air temperature/paddy water temperature) were maintained in [CO2] treatments of 330 and 660 μmol CO2 mol−1 air. In the 40/33/37°C temperature treatment, plants in the 330 μmol mol−1 [CO2] treatment died during stem extension while the [CO2] enriched plants survived but produced sterile panicles. Plants in the 34/27/31°C temperature treatments accumulated biomass and leaf area at a faster rate early in the growing season than plants in the 28/21/25°C temperature treatments. Tillering increased with increasing temperature treatment. Grain yield increases owing to [CO2] enrichment were small and non-significant. This lack of [CO2] response on grain yield was attributed to the generally lower levels of solar irradiance encountered during the late fall and winter when this experiment was conducted. Grain yields were affected much more strongly by temperature than [CO2] treatment. Grain yields declined by an average of approximately 7–8% per 1°C rise in temperature from the 28/21/25 to 34/27/31°C temperature treatment. The reduced grain yields with increasing temperature treatment suggests potential detrimental effects on rice production in some areas if air temperatures increase, especially under conditions of low solar irradiance.
Agricultural and Forest Meteorology.
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ABSTRACT: Carbon sequestration in soils might mitigate the increase of carbon dioxide (C(O)2) in the atmosphere. Two contrasting subtropical perennial forage species, bahiagrass (BG; Paspalum notatum Flugge; C4), and rhizoma perennial peanut (PP; Arachis glabrata Benth.; C3 legume), were grown at Gainesville, Florida, in field soil plots in four temperature zones of four temperature-gradient greenhouses, two each at C(O)2 concentrations of 360 and 700 micromol mol-1. The site had been cultivated with annual crops for more than 20 yr. Herbage was harvested three to four times each year. Soil samples from the top 20 cm were collected in February 1995, before plant establishment, and in December 2000 at the end of the project. Overall mean soil organic carbon (SOC) gains across 6 yr were 1.396 and 0.746 g kg-1 in BG and PP, respectively, indicating that BG plots accumulated more SOC than PP. Mean SOC gains in BG plots at 700 and 360 micromol mol-1 C(O)2 were 1.450 and 1.343 g kg-1, respectively (not statistically different). Mean SOC gains in PP plots at 700 and 360 micromol mol-1 C(O)2 were 0.949 and 0.544 g kg-1, respectively, an increase caused by elevated C(O)2. Relative SON accumulations were similar to SOC increases. Overall mean annual SOC accumulation, pooled for forages and C(O)2 treatments, was 540 kg ha-1 yr-1. Eliminating elevated C(O)2 effects, overall mean SOC accumulation was 475 kg ha-1 yr-1. Conversion from cropland to forages was a greater factor in SOC accumulation than the C(O)2 fertilization effect.
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ABSTRACT: The purpose of this study was to test for direct inhibition of rice canopy apparent respiration by elevated atmospheric carbon dioxide concentration ([CO2]) across a range of short-term air temperature treatments. Rice (cv. IR-72) was grown in eight naturally sunlit, semiclosed, plant growth chambers at daytime [CO2] treatments of 350 and 700 μmol mol-1. Short-term night-time air temperature treatments ranged from 21 to 40 °C. Whole canopy respiration, expressed on a ground area basis (Rd), was measured at night by periodically venting the chambers with ambient air. This night-time chamber venting and resealing procedure produced a range of increasing chamber [CO2] which we used to test for potential inhibitory effects of rising [CO2] on Rd. A nitrous oxide leak detection system was used to correct Rd measurements for chamber leakage rate (L) and also to determine if apparent reductions in night-time Rd with rising [CO2] could be completely accounted for by L. The L was affected by both CO2 concentration gradient between the chamber and ambient air and the inherent leakiness of each individual chamber. Nevertheless, after correcting Rd for L, we detected a rapid and reversible, direct inhibition of Rd with rising chamber [CO2] for air temperatures above 21 °C. This effect was larger for the 350 compared with the 700 μmol mol-1 daytime [CO2] treatment and was also increased with increasing short-term air temperature treatments. However, little difference in Rd was found between the two daytime [CO2] treatments when night-time [CO2] was at the respective daytime [CO2]. These results suggest that naturally occurring diurnal changes in both ambient [CO2] and air temperature can affect Rd. Because naturally occurring diurnal changes in both [CO2] and air temperature can be expected in a future higher CO2 world, short-term direct effects of these environmental variables on rice Rd can also be expected.
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ABSTRACT: Genetic modifications of agronomic crops will likely be necessary to cope with global climate change. This study tested the hypotheses that genotypic differences in rice (Oryza sativa L.) leaf photosynthesis at elevated [CO2] and temperature are related to protein and gene expression of Rubisco, and that high growth temperatures under elevated [CO2] negatively affect photosystem II (PSII) photochemical efficiency. Two rice cultivars representing an indica (cv. IR72) and japonica type (cv. M103) were grown in 350 (ambient) and 700 (elevated) micromol CO2 mol-1 at 28/18, 34/24 and 40/30 °C sinusoidal maximum/minimum, day/night temperatures in outdoor, sunlit, environment-controlled chambers. Leaf photosynthesis of IR72 favoured higher growth temperatures more than M103. Rubisco total activity and protein content were negatively affected in both genotypes by high temperatures and elevated CO2. However, at moderate to high growth temperatures, IR72 leaves averaged 71 and 39% more rbcS transcripts than M103 under ambient and elevated CO2, respectively, and likewise had greater Rubisco activity and protein content. Expression of psbA (D1 protein of PSII) in IR72 leaves increased with temperature, whereas it remained constant for M103, except for a 20% decline at 40/30 °C under elevated CO2. Even at the highest growth temperatures, PSII photochemical efficiency was not impaired in either genotype grown under either ambient or elevated CO2. Genotypic differences exist in rice for carboxylation responses to elevated CO2 and high temperatures, which may be useful in developing genotypes suited to cope with global climate changes.
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ABSTRACT: Soybean (Glycine max L. Merr. cv. Bragg) was grown season-long in eight sunlit, controlled-environment chambers at two daytime [CO2] of 350 (ambient) and 700 (elevated) micromol mol(-1). Dry bulb day/night maximum/minimum air temperatures, which followed a continuously and diurnally varying, near sine-wave control set point that operated between maximum (daytime, at 1500 EST) and minimum (nighttime, at 0700 EST) values, were controlled at 28/18 and 40/30 degrees C for the ambient-CO2 plants, and at 28/18, 32/22, 36/26, 40/30, 44/34 and 48/38 degrees C for the elevated-CO2 plants. The objective was to assess the upper threshold tolerance of photosynthesis and carbohydrate metabolism with increasing temperatures at elevated [CO2], as it is predicted that air temperatures could rise as much as 4-6 degrees C within the 21st century with a doubling of atmospheric [CO2]. Leaf photosynthesis measured at growth [CO2] and temperature was greater for elevated-CO2 plants and was highest at 32/22 degrees C, but markedly declined at temperatures above 40/30 degrees C. Growth temperatures from 28/18 to 40/30 degrees C had little effect on midday total activity and protein content of Rubisco, while higher temperatures substantially reduced them. Conversely, midday Rubisco rbcS transcript abundance declined with increasing temperatures from 28/18 to 48/38 degrees C. Elevated-CO2 plants exceeded the ambient CO2 plants in most aspects of carbohydrate metabolism. Under elevated [CO2], midday activities of ADPG pyrophosphorylase and sucrose-P synthase and invertase paralleled net increases in starch and sucrose contents, respectively. They were highest at 36/26-40/30 degrees C, but declined at higher or lower growth temperatures. Thus, in the absence of other climatic stresses, soybean photosynthesis and carbohydrate metabolism would perform well under rising atmospheric [CO2] and temperature predicted for the 21st century.
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ABSTRACT: Climate change due to increased [CO2] and elevated temperature may impact the composition of crop seed. This study was conducted to determine the potential effects of climate change on composition and gene expression of soybean [Glycine max (L.) Merr. cv. 'Bragg'] seed. Soybean plants were grown in sunlit, controlled environment chambers under diel, sinusoidal temperatures of 28/18, 32/22, 36/26, 40/30, and 44/34 degrees C (day/night, maximum/minimum), and two levels of [CO2], 350 and 700 micromol mol(-1), imposed during the entire life cycle. The effect of temperature on mature seed composition and transcripts in developing seed was pronounced, but there was no effect of [CO2]. Total oil concentration was highest at 32/22 degrees C and decreased with further increase in temperature. Oleic acid concentration increased with increasing temperature whereas linolenic acid decreased. Concentrations of N and P increased with temperature to 40/30 degrees C, then decreased. Total nonstructural carbohydrates (TNC) decreased as temperatures increased, and the proportion of soluble sugars to starch decreased. Transcripts of a gene that is downregulated by auxin (ADR12) were dramatically downregulated by elevated temperature, possibly reflecting the altered course of seed development under environmental stress. Transcripts of beta-glucosidase, a gene expressed during normal soybean seed development, were detected in seed grown at 28/18 degrees C but not in seed grown at 40/30 degrees C, which also suggests that normal programs affecting seed composition were perturbed by elevated temperature. These results confirm previous studies indicating that high temperature alters soybean seed composition, and suggest possible mechanisms by which climate change may affect soybean seed development and composition.
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Agronomy Journal. 88:704-716.
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ABSTRACT: Atmospheric carbon dioxide concentration [CO2] will increase in the future and will affect global climate and ecosystem productivity. Crop models used in past assessments of climate change effect on ecosystem productivity have not been adequately tested for the ability to simulate ecosystem responses to [CO2]. Our objective was to evaluate the ability of the default CROPGRO-Soybean model to predict the responses of net leaf photosynthesis (A) and canopy photosynthesis (A(can)) to photosynthetic photon flux (PPF) at different [CO2]. We also compared the default leaf photosynthesis equations in CROPGRO with the full Farquhar equations for ability to predict the response of A to [CO2]. Simulated and observed A and A(can) were light saturated at 800 micromol m(-2) s(-1) PPF at ambient [CO2] but did not light saturate at PPF >1100 micromol m(-2) s(-1) at elevated [CO2]. Observed and simulated A responded asymptotically to increasing intercellular [CO2]. The CROPGRO default photosynthesis equations and the Farquhar equations simulated A equally well at all [CO2]. Doubled [CO2] increased simulated A by 52% and A(can) by 42%; these values are close to the increases of 39 to 48% for A and 59% for A(can) reported in the literature. Root mean square errors for simulated A and A(can) were low, and Willmott's index of agreement ranged from 0.86 to 0.99, confirming that the CROPGRO model with default photosynthesis equations can be used to evaluate potential effects of [CO2] on soybean photosynthesis and productivity.
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ABSTRACT: Atmospheric CO2 and temperature may significantly modify plant production. Grasslands occupy in excess of 25% of the Earth's land area, but grassland species have received limited attention from researchers studying climate change. A 3-yr study was conducted to determine the effects of elevated atmospheric CO2 and temperature on dry matter (DM) harvested from the C3 legume 'Florigraze' rhizoma peanut (RP, Arachis glabrata Benth.) and the C4 grass 'Pensacola' bahiagrass (BG, Paspalum notatum Flugge). Both species were field grown in Millhopper fine sand (loamy siliceous Grossarenic Paleudult) in temperature-gradient greenhouses under different CO2 (360 and 700 micromol mol-1) and temperature conditions (baseline [B], B + 1.5, B + 3.0, and B + 4.5 degrees C, where B equaled ambient temperature). Plots (2 by 5 m) were harvested three times in 1996 and four times each in 1997 and 1998. Analyzed across years, yield increased 25% for RP (P = 0.02) and tended to increase for BG (15%; P = 0.18) with the near doubling of CO2, but there was species by CO2 interaction (P = 0.06) as a result of the greater response to CO2 by the C3 legume. There was a positive effect of increasing temperature on yield of both species. Averaged across species, yield increased 11% in 1996, 12% in 1997, and 26% in 1998 as temperature increased from B to B + 4.5 degrees C. Under well-watered conditions in this experiment, elevated CO2 increased DM harvested of a C3 legume and tended to increase that of a C4 grass, while the yield response to increasing temperature was positive for both species.
